Texture, mineralogy, carbon, nitrogen and phosphorus of Visakhapatnam shelf sediments, east coast of India

Abstract

Based on texture and grain size parameters, the study area is divided into near coastal region comprising of marginal high energy area with predominantly sand (up to 20 ml depth contour), and innershelf region comprising of marginal low energy region with sand-silt-clay (20 to 40 m depth contour). Heavy mineral assemblages indicate dominant occurrence of opaques, amphiboles, pyroxenes, garnets, sillimanite and mica, and minor proportions of monazite, epidote, zircon. The abundance of clay minerals followed the order montomorillonite > illite > kaolinite > chlorite. Seasonal variation of C, N and P are attributed to the fresh water influx and land runoff in monsoon (June-November) and intense photosynthetic activity in post (December-February)/premonsoon (March-May) seasons. Further, their increasing trend from coast to innershelf sediments is explained on the basis of their fine texture in the latter.